The major objective of this project is to advance our understanding of the physiology of steroid-gonadotropin relationships, with particular attention to elucidating quantitative parameters by simultaneous measurements of steroid and gonadotropin levels. Among more specific objectives are to study hypothalamo-pituitary interactions in relation to this system and the effects of stress and aging on the pituitary-testicular axis. These objectives will be pursued by studying gonadotropin and testosterone levels in rats, following destruction of specific hypothalamic nuclei; administration of LHRH by injection and infusion and of testosterone by implantation of constant release (Silastic) capsules; and application of various environmental stresses.